Alpha,omega-hydroxy-functionalized oligoester as adhesion promoter in aqueous basecoats

Abstract

Pigmented aqueous basecoat material comprises at least one alpha, omega-hydroxy-functionalized oligoester having an OH number of 25 to 95 mg KOH/g, a theoretical carbon-carbon double bond content of 0.5 to 2.5 mmol/g, a number-average molecular weight of 2500 to 6000 g/mol and a weight-average molecular weight of 15 000 to 30 000 g/mol, the alpha, omega-hydroxy-functionalized oligoester further comprising at least one partially or completely salified acid group, and the sum of the weight percentage fractions of all the alpha, omega-hydroxy-functionalized oligoesters being 0.5 to 10 wt %, based on the total solids fraction of the pigmented aqueous basecoat material. Also provided are a multicoat paint system, a method of producing a multicoat paint system, and use of the above-identified alpha, omega-hydroxy-functionalized oligoester in pigmented aqueous basecoat materials for the purpose of improving adhesion.

The invention claimed is: 
     
       1. A pigmented aqueous basecoat material comprising: at least one alpha, omega-hydroxy-functionalized oligoester which possesses an OH number of 25 to 95 mg KOH/g, a theoretical carbon-carbon double bond content of 0.5 to 2.5 mmol/g, a number-average molecular weight of 2500 to 6000 g/mol and a weight-average molecular weight of 15 000 to 30 000 g/mol, the alpha, omega-hydroxy-functionalized oligoester further comprising at least one partially or completely salified acid group, and the sum of the weight percentage fractions of all the alpha, omega-hydroxy-functionalized oligoesters being 0.5 to 10 wt %, based on the total solids fraction of the pigmented aqueous basecoat material. 
     
     
       2. The pigmented aqueous basecoat material according to  claim 1 , wherein the sum of the weight percentage fractions of all the alpha, omega-hydroxy-functionalized oligoesters is 1.5 to 7.5 wt %, based on the total solids fraction of the pigmented aqueous basecoat material. 
     
     
       3. The pigmented aqueous basecoat material according to  claim 1 , wherein the at least one alpha, omega-hydroxy-functionalized oligoester is the reaction product of:
 (i) at least one alpha, omega-hydroxy-functionalized oligoester (I) which possesses an OH number of 30 to 170 mg KOH/g, a theoretical carbon-carbon double bond content of 1 to 2.5 mmol/g, a number-average molecular weight of 800 to 2200 g/mol and a mass-weighted molecular weight of 1000 to 6000 g/mol, 
 (ii) with at least one cyclic dicarboxylic anhydride of the structural formula (I): 
 
       
         
           
           
               
               
           
         
         wherein B is an aliphatic or aromatic radical which contains at least one acid group, 
         with the proviso that the carboxylic acid groups resulting from the opening of the dicarboxylic anhydride group of the cyclic dicarboxylic anhydride of the structural formula (I) are reacted completely with the alpha, omega-hydroxy-functionalized oligoester (I), to form an ester bond in each case, and 
         (iii) the at least one acid group is partially or completely salified. 
       
     
     
       4. The pigmented aqueous basecoat material according to  claim 1 , wherein the alpha, omega-hydroxy-functionalized oligoester possesses the structural formula (II): 
       
         
           
           
               
               
           
         
         where 
         the (m+n+2) radicals R 1  independently of one another are selected from the group of linear or cyclic alkylene radicals, 
         the (m+n) radicals R 2  independently of one another are selected from the group of alkylene or alkenylene radicals, the ratio of alkylene to alkenylene radicals being just selected such that the alpha, omega-hydroxy-functionalized oligoester of the structural formula (II) possesses a theoretical carbon-carbon double bond content of 0.5 to 2.5 mmol/g, 
         the indices m and n are selected such that the number-average molecular weight of said alpha,omega-hydroxy-functionalized oligoester of the structural formula (II) is 2500 to 6000 g/mol, and 
         the radical B is an aliphatic or aromatic radical which contains at least one acid group which is partially or completely salified. 
       
     
     
       5. The pigmented aqueous basecoat material according to  claim 4 , wherein the alpha, omega-hydroxy-functionalized oligoester of the structural formula (II) possesses a number-average molecular weight of 3500 to 4500 g/mol. 
     
     
       6. The pigmented aqueous basecoat material according to  claim 4 , wherein the alpha, omega-hydroxy-functionalized oligoester of the structural formula (II) possesses a weight-average molecular weight of 20 000 to 26 000 g/mol. 
     
     
       7. The pigmented aqueous basecoat material according to  claim 5 , wherein the (m+n) radicals R 2  of the structural formula (II) are selected from the group consisting of linear alkylene radicals having 4 to 8 carbon atoms and linear alkenylene radicals having 2 to 4 carbon atoms. 
     
     
       8. The pigmented aqueous basecoat material according to  claim 5 , wherein the (m+n+2) radicals R 1  of the structural formula (II) are selected from the group consisting of linear alkylene radicals having 6 to 10 carbon atoms. 
     
     
       9. The pigmented aqueous basecoat material according to  claim 5 , wherein the (m+n+2) radicals R 1  of the structural formula (II) are selected from the group consisting of linear alkylene radicals having 6 to 10 carbon atoms and cyclic alkylene radicals having 6 to 10 carbon atoms. 
     
     
       10. The pigmented aqueous basecoat material according to  claim 5 , wherein the radical B is a radical
   A(Q) K , 
 wherein 
 A is an aliphatic or aromatic radical, 
 the radical Q is a partially or completely salified acid group, and 
 K=1 to 3. 
 
     
     
       11. The pigmented aqueous basecoat material according to  claim 10 , wherein A is a benzene radical, in which the two carboxylic ester groups of structural formula (II) are each located in alpha-position to one another, and K=1. 
     
     
       12. The pigmented aqueous basecoat material according to  claim 11 , wherein Q is a partially or completely salified carboxylic acid group. 
     
     
       13. A multicoat paint system on a plastics substrate, comprising one above another in this order:
 (A) at least one first coat, resulting from the application of the pigmented aqueous basecoat material according to  claim 1 , and 
 (B) at least one second, transparent coat. 
 
     
     
       14. A method for producing a multicoat paint system on a plastics substrate, comprising:
 (A) applying the pigmented aqueous basecoat material according to  claim 1  to a plastics substrate, to give a first coat, 
 (B) drying the coat applied in (A), 
 (C) applying a second, transparent coat, and 
 (D) jointly curing the coats applied in (A) and (C). 
 
     
     
       15. A method for improving adhesion in a pigmented aqueous basecoat material comprising:
 mixing at least one alpha, omega-hydroxy-functionalized oligoester having an OH number of 25 to 95 mg KOH/g, a theoretical carbon-carbon double bond content of 0.5 to 2.5 mmol/g, a number-average molecular weight of 2500 to 6000 g/mol and a weight-average molecular weight of 15 000 to 30 000 g/mol, the alpha, omega-hydroxy-functionalized oligoester further comprising at least one partially or completely salified acid group, and the sum of the weight percentage fractions of all the alpha, omega-hydroxy-functionalized oligoesters being 0.5 to 10 wt %, based on the total solids fraction of the pigmented aqueous basecoat material with one or more pigmented aqueous basecoat material components to form the pigmented aqueous basecoat material.